1. Field of the Invention
Exemplary embodiments of the invention relate to a backlight unit, and more particularly, to a backlight unit of which the weight is easy to decrease.
2. Description of the Related Art
Liquid crystal displays have been used in notebook personal computers, office automatic equipments, audio/video equipments, etc. because of advantages such as miniaturization, thin profile, and low power consumption.
The liquid crystal display includes a liquid crystal display module and a backlight unit. The backlight unit may be classified into an edge type backlight unit and a direct-under type backlight unit depending on a location of a light source.
The edge type backlight unit includes a light source unit, a light guide plate, a reflective plate, and an optical film.
The light source unit includes a light source such as at lest one cold cathode fluorescent lamp (CCFL) and at lest one external electrode fluorescent lamp (EEFL), and a light source reflective plate on which the light source is positioned.
The light source produces light having a predetermined wavelength, for example, white light. The light source reflective plate reflects the light produced by the light source.
The light guide plate is positioned at the side of the light source unit so as to obtain uniform light. The light guide plate allows the light coming from the light source unit to travel toward the liquid crystal display module.
The light guide plate is made of acrylic material having a critical angle of about 42° and a refractive index of about 1.5. The light guide plate is formed in a plate shape having an upper surface, a lower surface, and 4 sides.
Accordingly, in light passing through the side (i.e., an incident surface) of the light guide plate facing the light source unit, light having an azimuth angle smaller than the critical angle is emitted through the upper surface of the light guide plate, and light having an azimuth angle equal to or larger than the critical angle is totally reflected and diffused on the entire surface of the light guide plate.
The reflective plate is positioned on the lower surface of the light guide plate to reflect leakage light in an inside space of the light guide plate. The lower surface of the light guide plate may has a scattering pattern.
The optical film includes a diffuser sheet, a prism sheet, and a protective sheet. The diffuser sheet is positioned on the light guide plate and may include a lower diffuser sheet, a diffuser sheet support unit, and an upper diffuser sheet.
The diffuser sheet diffuses light traveling through the light guide plate using beads distributed in the diffuser sheet.
The prism sheet is positioned on the diffuser sheet and includes a base film and prisms. The prism sheet focuses the light diffused by the diffuser sheet.
The protective sheet diffuses the light focused by the prism sheet to provide the diffused light to the liquid crystal display module.
In addition to the above-described configuration of the optical film, the optical film may use combinations of various sheets in order to diffuse and focus the light traveling through the light guide plate.
In the edge-type backlight unit, the light guide plate is formed using an injection molding method or an extrusion molding method. In particular, the light guide plate is formed by forming a base using an injection molding method or an extrusion molding method and then forming a scattering pattern on a lower surface of the base through a curing process such as a thermal curing method. The weight of the light guide plate occupies most of the total weight of the edge-type backlight unit.
Accordingly, it is necessary to reduce a reduction in a thickness of the light guide plate in order to reduce the weight of the backlight unit and the weight of the liquid crystal display. However, it is limited to reduce the thickness of the light guide plate because of the light use efficiency. After all, the reduction in the weight of the backlight unit has been in the face of technical limitation.